1. Field of the Invention
This application is related to integrated circuits and, more particularly, to amplifier circuits.
2. Description of the Related Art
In general, an operational transconductance amplifier (i.e., “unbuffered” operational amplifier) is an amplifier circuit that has a very high output resistance and generates an output current in response to a differential input voltage. Thus, the operational amplifier is a voltage controlled current source (VCCS). In an ideal operational transconductance amplifier, the output current is a linear function of the differential input voltage, i.e., IOUT=(VIN+−VIN−)×gm, where VIN+ is a voltage at a non-inverting input, VIN− is a voltage at the inverting input, and gm is the transconductance of the amplifier. A typical operational amplifier has a high impedance differential input stage and may be used with or without negative feedback. Performance limitations of a typical operational transconductance amplifier include insufficient gain, limited stable bandwidth caused by an inability to control higher-order poles of the operational transconductance amplifier, and poor power-supply rejection.